1). Field of the Invention
Embodiments of this invention relate to a method for the formation of contact formations, particularly for use on semiconductor substrates and a system utilizing such contact formations.
2). Discussion of Related Art
Integrated circuits are formed on semiconductor substrates, such as wafers. The wafers are then sawed (or “singulated” or “diced”) into microelectronic dice, also known as semiconductor chips, with each chip carrying a respective integrated circuit. Each semiconductor chip is then mounted to a package, or carrier, substrate. Often the packages are then mounted to circuit boards, such as motherboards, which may then be installed in computing systems.
The package substrates provide structural integrity to the semiconductor chips and are used to connect the integrated circuits electrically to the motherboard. On the side of the package substrate connected to the motherboard, there are contact formations, such as Ball Grid Array (BGA) solder balls, which are soldered to the motherboard. Electric signals are sent through the BGA solder balls into and out of the package. On the other side of the package substrate, there are other, smaller contact formations used to connect the dice to the package substrate. A modern trend for these contact formations is the use of “copper bumps” which are formed on bonding pads on the dice. An underfill material, such as an epoxy or paste, may also be present between the dice and the packages.
Copper bumps are typically formed using an electroplating process. The formation of the bumps begins within a depression on the surface of the dice. This depression leads to a “dimple,” or other formations, on the surface of the copper bumps opposite the dice. It is this dimpled surface which is used to connect the dice to the packages.
This dimple is undesirable because it allows material, such as solder, underfill material, or even air, to get caught between the copper bump and the package substrate when the chip-to-package connections are made. This trapped material weakens the strength of the mechanical bond between the dice and package substrates and results in a decease in the maximum amount of current that can be conducted through the copper bumps.